The present invention relates to a functional material, a dispersion containing the functional material, and a process for producing the functional material. More particularly, the present invention relates to a functional material composed of fine coloring particles, which exhibits not only an excellent transparency but also a high tinting strength and a clear hue, a dispersion containing the functional material, and a process for producing the functional material.
As well known in the art, organic pigments have been used as colorants for paints, resins, printing inks or the like according to applications thereof. Therefore, the organic pigments have been generally required to have a high tinting and a good transparency.
The organic pigments are produced by first forming fine primary particles having a particle size as small as about 20 to 100 nm from the pigments in a molecular state produced by a chemical reaction, and then subjecting the thus obtained primary particles to filtering, washing and drying steps. However, the fine primary particles tend to be agglomerated because of a very high surface energy thereof, thereby forming aggregates (secondary particles). It is well known that the formation of the secondary particles remarkably proceeds, in particular, upon the drying step.
The organic pigments in the form of fine coloring particles have a possibility of exhibiting novel functions. Therefore, it has been expected that the organic pigments are used in other applications than pigments, for example, as nonlinear optical materials.
As the method for producing such fine coloring particles, there are known, for example, a method of applying an ultrasonic wave to a liquid dispersion containing fine functional particles dispersed therein to inhibit agglomeration thereof (Japanese Patent Application Laid-open No. 11-269432(1999)); and a method of producing fine coloring particles of an organic compound by irradiating a laser beam to the organic compound (Japanese Patent Application Laid-open No. 2001-113159).
However, in any of these conventional methods, it may be difficult to obtain fine coloring particles having a primary particle diameter of not more than 50 nm. At present, it has been strongly required to provide fine coloring particles having a high tinting strength as well as an excellent transparency and a clear hue. However, the conventional methods have failed to obtain such fine coloring particle satisfying the above properties.
As a result of the present inventors' earnest studies, it has been found that by mixing inorganic compound particles with a gluing agent under stirring to form a gluing agent coat on the surface of the inorganic compound particles, mixing organic pigments with the obtained inorganic compound particles coated with the gluing agent under stirring to adhere the organic pigments onto the surface of the gluing agent coat, thereby obtaining composite particles, and then dissolving either the inorganic compound particles as core particles only or both of the inorganic compound particles and the gluing agent from the composite particles, the obtained functional material composed of fine coloring particles have a fine primary particle diameter, and can exhibit a high tinting strength as well as an excellent transparency and a clear hue. The present invention has been attained on the basis of this finding.